Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description states it is 'Deterministic, cites primary sources; errors and unverified rules are never billed,' which gives some reliability context. However, without annotations, it lacks explicit side-effect info, output structure, or authentication requirements. It does not mention whether the tool is read-only or has other hidden behaviors.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two short sentences, front-loaded with the core functionality. It includes cost and reliability in a compact manner with no fluff. Every word serves a purpose, making it highly concise and well-structured.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

This is a complex tool with 6 parameters, nested objects, a payment mechanism, and no output schema. The description is minimal, lacking parameter explanations, output details, usage prerequisites, and how the x_payment system interacts with the tool. Given the complexity, a much richer description is needed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is only 17% (only x_payment has a description). The description mentions 'level payment/principal' and 'prepayment effect' but does not map these to the actual parameters like method or prepayment. It fails to explain principal_yen, annual_rate, months, method, or how the nested objects are used, leaving agents without essential parameter meaning.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function: 'Mortgage schedules (level payment/principal), total interest, prepayment effect.' This provides a specific verb and resource scope, indicating exactly what the tool computes. The cost and reliability details are secondary yet reinforce the purpose.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description offers no guidance on when to use this tool, prerequisites, or how it relates to other sibling tools. It does not suggest alternatives or explain scenarios where this is appropriate. The only operational detail is the $0.005/call cost, which is not usage guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.